Total Syntheses of Allelopathic 4‑Oxyprotoilludanes, Melleolides, and Echinocidins

Stereocontrolled
total syntheses of allelopathic 4-oxyprotoilludane
sesquiterpenes, melleolide, melleolide F, and echinocidins B and D
were achieved. The curved 5/6/4 tricyclic system with an angular hydroxy
group was built via three key transformations: (1) Me3Al-catalyzed
[2 + 2] cycloaddition of a ketene silyl acetal with a propiolate,
(2) reductive ring-opening of a cyclic hemiketal, and (3) the intramolecular
Morita–Baylis–Hillman reaction. This synthetic route
represents a new and reliable strategy to obtain protoilludanes with
several oxy-functional groups.